The invention generally concerns hydrodynamic torque converters.
A conventional hydrodynamic torque converter typically includes a converter housing rotatably mounted on a shaft and which is connected to a drive and to a pump wheel or impeller. A turbine wheel is supported rotatably relative to the converter housing and is coupled to the shaft and hydrodynamically to the impeller. The torque converter further includes a bridging or lockup clutch to produce a friction coupling between a friction surface operably associated with the converter housing and a friction surface operably associated with the turbine.
Such a hydrodynamic torque converter can be used more particularly in a motor vehicle in order to transmit torque produced by an internal combustion engine to a transmission or to the wheels of the vehicle by way of a shaft. A typical torque converter of that general kind is to be found for example in WO 93/13338. The converter housing of that torque converter, which is mounted rotatably about the shaft as referred to above, is connected to a drive coming from the internal combustion engine, while in its interior it has the impeller or pump wheel that is fixedly connected to the converter housing. The arrangement of the turbine wheel which is supported rotatably on the shaft relative to the converter housing and a stator operatively disposed between the turbine and the impeller is such that, when the converter housing is rotated by the drive from the internal combustion engine, a hydrodynamic pressure is built up in the oil filling in the converter, and a circulatory flow of the oil by way of the impeller, the stator and the turbine takes place. Suitable shaping of the vanes of the impeller, stator and turbine, and supporting the stator by way of a freewheel unit, provides an increase in torque when the vehicle starts moving. In addition, the hydrodynamic coupling between the engine drive and the output shaft permits a gentle start without a clutch, and fluctuations in torque from the internal combustion engine can be appropriately damped.
The torque converter of above-mentioned WO 93/13338 also includes a bridging or lockup clutch. When the converter housing with the impeller and the turbine driven thereby with its shaft have reached approximately the same speed of rotation, the lockup clutch can be closed to produce a force-locking mechanical coupling between the converter housing and the shaft. In that way, in what is referred to as the clutch range in which the engine drive and the shaft are rotating at approximately the same speed, the hydrodynamic coupling, which suffers from an energy loss in that situation, is replaced by a mechanical coupling action. In that arrangement the lockup clutch is embodied by one or more friction surfaces with associated counterpart surfaces, of which one is associated with the converter housing and the other to the turbine. In order to engage the lockup clutch the two friction surfaces, which are disposed in mutually opposite relationship at an axial spacing in the inoperative condition of the clutch, are brought into contact with each other whereby the converter housing and the turbine are coupled together.
From the point of view of the structure involved, the lockup clutch in a torque converter as in WO 93/13338 is embodied by the provision of a disk-shaped member which is referred to as a piston and which is axially slidably supported on the shaft and non-rotatably connected to the converter housing. The piston has a first friction surface disposed thereon, which is in opposite relationship to a second friction surface provided on the converter housing.
Disposed between those two friction surfaces is a coupling element connected by way of a torsion damper to the turbine. In the opened or disengaged condition of the lockup clutch, the friction surfaces on the piston and the converter housing on the one hand and on the coupling element on the other hand are spaced from each other so that no coupling action takes place therebetween. In the closed or engaged condition of the lockup clutch on the other hand the piston is to be displaced axially towards the cover part of the converter housing which is at the engine side, and thereby clamps the coupling element disposed between it and the converter housing. As a result, the corresponding friction surfaces come into contact with each other so that the coupling element affords a force-locking frictional coupling effect between the converter housing and the turbine.
As already mentioned above, the coupling element in the torque converter of WO 93/13338 is coupled to the turbine by way of a torsion damper. That torsion damper comprises coil springs that extend in the peripheral direction of the converter and which are mounted to the outer shell portion of the turbine, one end of the coil springs being supported on the turbine and the other end on the coupling element. The springs are thus connected in serial relationship into the path of the flow of force from the coupling element to the turbine and provide that torque peaks and fluctuations originating from the drive or the converter housing can be appropriately damped and compensated as they are passed to the turbine and to the shaft respectively.
Therefore, a first object of the invention is to simplify the design of a hydrodynamic torque converter with lockup clutch so as to afford a more compact structure and reduced production costs together with a lower susceptibility to faults.
Another object of the present invention is to provide a hydrodynamic torque converter with lockup clutch which is of a more rational construction and an enhanced mode of operation with the elimination of some potential area of wear.
Still another object of the present invention is to provide a hydrodynamic torque converter incorporating a lockup clutch, so as to afford a mechanically simple operating procedure for engagement of the lockup clutch.
In accordance with the principles of the present invention, the foregoing and other objects are attained by a hydrodynamic torque converter including a converter housing which is rotatable about a shaft, and which is connected to a drive such as an internal combustion engine, and to an impeller. A turbine is supported rotatably relative to the converter housing, is coupled to the shaft, and is hydrodynamically coupled to the impeller. A lockup clutch produces friction coupling between a friction surface operably associated with the converter housing and a friction surface operably associated with the turbine. The turbine is axially slidably supported, whereby axial sliding movement of the turbine causes the friction surfaces to be brought into contact with each other.
As will be seen from a description hereinafter of preferred embodiments of the invention, the hydrodynamic torque converter according to the invention provides that an input torque coming from a suitable drive is hydrodynamically transmitted by way of the converter housing and the impeller to the turbine, which delivers the torque in converted mode to the output by way of the shaft. By way of the lockup clutch, mechanical coupling between the converter housing and the turbine can be produced in parallel with or alternatively to the hydrodynamic coupling condition, when the friction surfaces have been brought into contact with each other.
As in accordance with the invention, contact is made between those friction surfaces and thus the lockup clutch is closed by axial sliding movement of the turbine. Therefore, there is accordingly no need to provide an additional axially slidably mounted element, as referred to in the prior constructions, and this elimination of such an element can reduce the structural complication and expenditure, and thus reduce the production costs of the torque converter, avoid a potential wear point, and make it possible for the torque converter to be of a more compact configuration.
In this respect, the hydrodynamic coupling action which may possibly occur between the impeller and the turbine, due to the axial displacement of the turbine, does not result in any detrimental effects in terms of the transmission characteristics of the torque converter as, when the lockup clutch is closed or engaged, the hydrodynamic coupling effect is in any case not being used.
In accordance with a preferred feature of the invention the hydrodynamic torque converter includes a torsion damper for dampening the torque transmission between the drive and the shaft. That makes it possible to compensate for and equalise torque peaks and shocks and fluctuations in the torque produced by the engine, and this arrangement makes it possible to provide a smooth torque delivery.
In a first configuration in accordance with that feature, the torsion damper is arranged in the force-transmitting connection between the turbine and the associated friction surface of the lockup clutch. In other words, the torsion damper dampens the torque transmitted to that friction surface when the lockup clutch is engaged, before the torque is transmitted to the turbine. That arrangement provides for a more gentle engagement characteristic on the part of the lockup clutch as well as absorbing torque peaks and fluctuations when the lockup clutch engaged. In contrast, when the lockup clutch is open or disengaged, the torsion damper is out of operation so that the torque hydrodynamically transmitted from the impeller to the turbine is transmitted unchanged to the shaft.
In accordance with another configuration of this feature the torsion damper is operably disposed between the turbine and the shaft. In that position, it dampens the transmission of torque from the turbine to the shaft, irrespective of whether the torque is being transmitted hydrodynamically by the impeller or by engagement of the lockup clutch to the turbine. Accordingly when the torsion damper is arranged as such, it affords general torque smoothing prior to the torque being delivered by way of the shaft.
In a further preferred feature of the invention, the torsion damper includes at least one peripherally extending spring mounted to the outer shell portion of the turbine, the spring having one end supported on the turbine and another end supported on a coupling element that is rotatable relative to the turbine. Preferably, the torque converter has a plurality of such springs that are distributed in a symmetrical arrangement over the periphery of the turbine. By virtue of the way in which they are supported, the springs are disposed in serial relationship in the path of force transmission between the coupling element and the turbine so that they can implement smoothing of the torque by virtue of the resiliency of the springs. Relative rotary movement between the coupling element and the turbine can also be damped by friction according to the desired transmission characteristics.
In a preferred feature of the last-mentioned design configuration of the torsion damper, the coupling element has at least one peripherally extending slot, through which engages a projection protruding axially away from the outer shell portion of the turbine. The combination of the slot and the projection permits relative rotary movement as between the turbine and the coupling element, but that relative rotary movement is limited by virtue of the first and second ends of the slot butting against the projection protruding through the slot.
In a preferred feature, the torque converter has means for sealing the slot relative to the projection so that a pressure medium can be at different pressures on the two sides of the coupling element. A particularly simple form of such sealing means can provide that the coupling element lies flat and thus in a condition of sealing integrity against the outside of the turbine. Sealing integrity of the surfaces which are in a condition of bearing against each other is primarily achieved by clamping or bracing springs or other clamping or bracing elements which are fixed on the projection, which apply a predetermined force to the opposite side of the coupling element to brace the sealing surfaces into contact with each other. In addition, preferably in the region of engagement of the projection into the slot, it is possible to afford adjustable friction between the coupling element and the turbine, by means of which it is possible to set desired damping characteristics in the transmission path between the coupling element and the turbine.
In accordance with yet another preferred feature of the invention, the friction surface operably associated with the turbine is provided on the above-mentioned coupling element. With that design configuration, when the lockup clutch is closed, the coupling element is non-rotatably operably associated with the converter housing by way of the friction surface, and transmission of the torque from the coupling element to the turbine is smoothed out by virtue of the interposed torsion damper.
Another design configuration of the torque converter provides that the friction surface operably associated with the turbine is on the outer shell portion of the turbine. This means that the turbine can involve frictional contact with the converter housing directly by way of that friction surface, without the need for elements disposed therebetween. Implementing frictional contact between the turbine and the converter housing is made possible by virtue of the turbine being axially slidably mounted.
In a further preferred embodiment, at least one of the friction surfaces involved in the lockup clutch and which are operably associated with the turbine and to the converter housing respectively can be made from an aluminum-casting alloy. The material can be refined by the addition of various alloying constituents. Preferably, the friction surface operably associated with the turbine is made from the same material as the turbine, which preferably also comprises an aluminum-casting alloy.
In a preferred embodiment, a vacuum pressure casting process is used to produce the turbine.
As an alternative, the turbine and/or the converter housing may also be made from other casting materials or from plastic material.
Furthermore, in a preferred feature of the invention, at least one of the friction surfaces of the lockup clutch can be made from steel. In particular the combination of a friction surface comprising steel and a friction surface comprising aluminum alloy has advantageous sliding properties.
Furthermore, at least one of the friction surfaces may have oil flow passages through which the pressure medium in the interior of the torque converter can flow when the lockup clutch is closed or closing. That flow of pressure medium can positively influence the resulting frictional contact between the friction surfaces and can also dissipate frictional heat from the friction surfaces.
A preferred development of the invention provides that the torque converter has passages for a pressure medium, the arrangement being such that, by way of a suitable feed line for the pressure medium by way of those passages, the two sides of the turbine which face in different axial directions, constituting therefore a front side and a rear side, can be selectively acted upon by a pressure difference. Such a pressure difference makes it possible to apply an axially operative force to the turbine so as to cause an axial displacement of the turbine. The axial position of the turbine, and thus engagement and disengagement of the lockup clutch, can thus be controlled by suitably feeding pressure medium to the front side or to the rear side of the turbine.
In accordance with a further advantageous configuration of the invention, it is possible to provide on the turbine at least one piston means for frictionally coupling the turbine and the converter housing. In order to produce a condition of frictional coupling in that way, firstly a part of the torque is transmitted between the turbine and the converter housing by means of the piston means, in order thereby to facilitate the axial sliding movement of the turbine for definitively engaging the lockup clutch.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments of the invention.